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VINUM(8) FreeBSD System Manager's Manual VINUM(8)
NAMEvinum -- Logical Volume Manager control program
SYNOPSISvinum [command] [-options]
COMMANDSattachplexvolume [rename]
attachsubdiskplex [offset] [rename]
Attach a plex to a volume, or a subdisk to a plex.
checkparityplex [-f] [-v]
Check the parity blocks of a RAID-4 or RAID-5 plex.
concat [-f] [-nname] [-v] drives
Create a concatenated volume from the specified drives.
create [-f] description-file
Create a volume as described in description-file.
debug Cause the volume manager to enter the kernel debugger.
debugflags
Set debugging flags.
detach [-f] [plex | subdisk]
Detach a plex or subdisk from the volume or plex to which it is
attached.
dumpconfig [drive...]
List the configuration information stored on the specified
drives, or all drives in the system if no drive names are speci-
fied.
info [-v] [-V]
List information about volume manager state.
init [-Ssize] [-w] plex | subdisk
Initialize the contents of a subdisk or all the subdisks of a
plex to all zeros.
labelvolume
Create a volume label.
l | list [-r] [-s] [-v] [-V] [volume | plex | subdisk]
List information about specified objects.
ld [-r] [-s] [-v] [-V] [volume]
List information about drives.
ls [-r] [-s] [-v] [-V] [subdisk]
List information about subdisks.
lp [-r] [-s] [-v] [-V] [plex]
List information about plexes.
lv [-r] [-s] [-v] [-V] [volume]
List information about volumes.
makedev
Remake the device nodes in /dev/vinum.
mirror [-f] [-nname] [-s] [-v] drives
Create a mirrored volume from the specified drives.
move | mv-fdriveobject...
Move the object(s) to the specified drive.
printconfig [file]
Write a copy of the current configuration to file.
quit Exit the vinum program when running in interactive mode. Nor-
mally this would be done by entering the EOF character.
readdisk...
Read the vinum configuration from the specified disks.
rename [-r] [drive | subdisk | plex | volume] newname
Change the name of the specified object.
rebuildparityplex [-f] [-v] [-V]
Rebuild the parity blocks of a RAID-4 or RAID-5 plex.
resetconfig
Reset the complete vinum configuration.
resetstats [-r] [volume | plex | subdisk]
Reset statistics counters for the specified objects, or for all
objects if none are specified.
rm [-f] [-r] volume | plex | subdisk
Remove an object.
saveconfig
Save vinum configuration to disk after configuration failures.
setdaemon [value]
Set daemon configuration.
setstatestate [volume | plex | subdisk | drive]
Set state without influencing other objects, for diagnostic pur-
poses only.
start Read configuration from all vinum drives.
start [-iinterval] [-Ssize] [-w] volume | plex | subdisk
Allow the system to access the objects.
stop [-f] [volume | plex | subdisk]
Terminate access to the objects, or stop vinum if no parameters
are specified.
stripe [-f] [-nname] [-v] drives
Create a striped volume from the specified drives.
DESCRIPTIONvinum is a utility program to communicate with the vinum(4) logical vol-
ume manager. vinum is designed either for interactive use, when started
without command line arguments, or to execute a single command if the
command is supplied on the command line. In interactive mode, vinum
maintains a command line history.
OPTIONSvinum commands may optionally be followed by an option. Any of the fol-
lowing options may be specified with any command, but in some cases the
options are ignored. For example, the stop command ignores the -v and -V
options.
-f The -f (``force'') option overrides safety checks. Use with
extreme care. This option is for emergency use only. For exam-
ple, the command
rm -f myvolume
removes myvolume even if it is open. Any subsequent access to
the volume will almost certainly cause a panic.
-imillisecs
When performing the init and start commands, wait millisecs mil-
liseconds between copying each block. This lowers the load on
the system.
-nname
Use the -n option to specify a volume name to the simplified con-
figuration commands concat, mirror and stripe.
-r The -r (``recursive'') option is used by the list commands to
display information not only about the specified objects, but
also about subordinate objects. For example, in conjunction with
the lv command, the -r option will also show information about
the plexes and subdisks belonging to the volume.
-s The -s (``statistics'') option is used by the list commands to
display statistical information. The mirror command also uses
this option to specify that it should create striped plexes.
-Ssize
The -S option specifies the transfer size for the init and start
commands.
-v The -v (``verbose'') option can be used to request more detailed
information.
-V The -V (``Very verbose'') option can be used to request more
detailed information than the -v option provides.
-w The -w (``wait'') option tells vinum to wait for completion of
commands which normally run in the background, such as init.
COMMANDS IN DETAILvinum commands perform the following functions:
attachplexvolume [rename]
attachsubdiskplex [offset] [rename]
vinumattach inserts the specified plex or subdisk in a volume or
plex. In the case of a subdisk, an offset in the plex may be
specified. If it is not, the subdisk will be attached at the
first possible location. After attaching a plex to a non-empty
volume, vinum reintegrates the plex.
If the keyword rename is specified, vinum renames the object (and
in the case of a plex, any subordinate subdisks) to fit in with
the default vinum naming convention. To rename the object to any
other name, use the rename command.
A number of considerations apply to attaching subdisks:
+o Subdisks can normally only be attached to concatenated
plexes.
+o If a striped or RAID-5 plex is missing a subdisk (for example
after drive failure), it should be replaced by a subdisk of
the same size only.
+o In order to add further subdisks to a striped or RAID-5 plex,
use the -f (force) option. This will corrupt the data in the
plex.
+o For concatenated plexes, the offset parameter specifies the
offset in blocks from the beginning of the plex. For striped
and RAID-5 plexes, it specifies the offset of the first block
of the subdisk: in other words, the offset is the numerical
position of the subdisk multiplied by the stripe size. For
example, in a plex with stripe size 271k, the first subdisk
will have offset 0, the second offset 271k, the third 542k,
etc. This calculation ignores parity blocks in RAID-5
plexes.
checkparityplex [-f] [-v]
Check the parity blocks on the specified RAID-4 or RAID-5 plex.
This operation maintains a pointer in the plex, so it can be
stopped and later restarted from the same position if desired.
In addition, this pointer is used by the rebuildparity command,
so rebuilding the parity blocks need only start at the location
where the first parity problem has been detected.
If the -f flag is specified, checkparity starts checking at the
beginning of the plex. If the -v flag is specified, checkparity
prints a running progress report.
concat [-f] [-nname] [-v] drives
The concat command provides a simplified alternative to the
create command for creating volumes with a single concatenated
plex. The largest contiguous space available on each drive is
used to create the subdisks for the plexes.
Normally, the concat command creates an arbitrary name for the
volume and its components. The name is composed of the text
``vinum'' and a small integer, for example ``vinum3''. You can
override this with the -nname option, which assigns the name
specified to the volume. The plexes and subdisks are named after
the volume in the default manner.
There is no choice of name for the drives. If the drives have
already been initialized as vinum drives, the name remains. Oth-
erwise the drives are given names starting with the text
``vinumdrive'' and a small integer, for example ``vinumdrive7''.
As with the create command, the -f option can be used to specify
that a previous name should be overwritten. The -v is used to
specify verbose output.
See the section SIMPLIFIEDCONFIGURATION below for some examples
of this command.
create [-f] description-filevinumcreate is used to create any object. In view of the rela-
tively complicated relationship and the potential dangers
involved in creating a vinum object, there is no interactive
interface to this function. If you do not specify a file name,
vinum starts an editor on a temporary file. If the environment
variable EDITOR is set, vinum starts this editor. If not, it
defaults to vi. See the section CONFIGURATIONFILE below for
more information on the format of this file.
Note that the vinumcreate function is additive: if you run it
multiple times, you will create multiple copies of all unnamed
objects.
Normally the create command will not change the names of existing
vinum drives, in order to avoid accidentally erasing them. The
correct way to dispose of no longer wanted vinum drives is to
reset the configuration with the resetconfig command. In some
cases, however, it may be necessary to create new data on vinum
drives which can no longer be started. In this case, use the
create-f command.
debugvinumdebug, without any arguments, is used to enter the remote
kernel debugger. It is only activated if vinum is built with the
VINUMDEBUG option. This option will stop the execution of the
operating system until the kernel debugger is exited. If remote
debugging is set and there is no remote connection for a kernel
debugger, it will be necessary to reset the system and reboot in
order to leave the debugger.
debugflags
Set a bit mask of internal debugging flags. These will change
without warning as the product matures; to be certain, read the
header file <sys/dev/vinumvar.h>. The bit mask is composed of
the following values:
DEBUG_ADDRESSES (1)
Show buffer information during requests
DEBUG_RESID (4)
Go into debugger in complete_rqe().
DEBUG_LASTREQS (8)
Keep a circular buffer of last requests.
DEBUG_REVIVECONFLICT (16)
Print info about revive conflicts.
DEBUG_EOFINFO (32)
Print information about internal state when returning an
EOF on a striped plex.
DEBUG_MEMFREE (64)
Maintain a circular list of the last memory areas freed
by the memory allocator.
DEBUG_REMOTEGDB (256)
Go into remote gdb when the debug command is issued.
DEBUG_WARNINGS (512)
Print some warnings about minor problems in the implemen-
tation.
detach [-f] plexdetach [-f] subdiskvinumdetach removes the specified plex or subdisk from the vol-
ume or plex to which it is attached. If removing the object
would impair the data integrity of the volume, the operation will
fail unless the -f option is specified. If the object is named
after the object above it (for example, subdisk vol1.p7.s0
attached to plex vol1.p7), the name will be changed by prepending
the text ``ex-'' (for example, ex-vol1.p7.s0). If necessary, the
name will be truncated in the process.
detach does not reduce the number of subdisks in a striped or
RAID-5 plex. Instead, the subdisk is marked absent, and can
later be replaced with the attach command.
dumpconfig [drive...]
vinumdumpconfig shows the configuration information stored on
the specified drives. If no drive names are specified,
dumpconfig searches all drives on the system for Vinum partitions
and dumps the information. If configuration updates are dis-
abled, it is possible that this information is not the same as
the information returned by the list command. This command is
used primarily for maintenance and debugging.
infovinuminfo displays information about vinum memory usage. This
is intended primarily for debugging. With the -v option, it will
give detailed information about the memory areas in use.
With the -V option, info displays information about the last up
to 64 I/O requests handled by the vinum driver. This information
is only collected if debug flag 8 is set. The format looks like:
vinum -> info -V
Flags: 0x200 1 opens
Total of 38 blocks malloced, total memory: 16460
Maximum allocs: 56, malloc table at 0xf0f72dbc
Time Event Buf Dev Offset Bytes SD SDoff Doffset Goffset
14:40:00.637758 1VS Write 0xf2361f40 91.3 0x10 16384
14:40:00.639280 2LR Write 0xf2361f40 91.3 0x10 16384
14:40:00.639294 3RQ Read 0xf2361f40 4.39 0x104109 8192 19 0 0 0
14:40:00.639455 3RQ Read 0xf2361f40 4.23 0xd2109 8192 17 0 0 0
14:40:00.639529 3RQ Read 0xf2361f40 4.15 0x6e109 8192 16 0 0 0
14:40:00.652978 4DN Read 0xf2361f40 4.39 0x104109 8192 19 0 0 0
14:40:00.667040 4DN Read 0xf2361f40 4.15 0x6e109 8192 16 0 0 0
14:40:00.668556 4DN Read 0xf2361f40 4.23 0xd2109 8192 17 0 0 0
14:40:00.669777 6RP Write 0xf2361f40 4.39 0x104109 8192 19 0 0 0
14:40:00.685547 4DN Write 0xf2361f40 4.39 0x104109 8192 19 0 0 0
11:11:14.975184 Lock 0xc2374210 2 0x1f8001
11:11:15.018400 7VS Write 0xc2374210 0x7c0 32768 10
11:11:15.018456 8LR Write 0xc2374210 13.39 0xcc0c9 32768
11:11:15.046229 Unlock 0xc2374210 2 0x1f8001
The Buf field always contains the address of the user buffer
header. This can be used to identify the requests associated
with a user request, though this is not 100% reliable: theoreti-
cally two requests in sequence could use the same buffer header,
though this is not common. The beginning of a request can be
identified by the event 1VS or 7VS. The first example above
shows the requests involved in a user request. The second is a
subdisk I/O request with locking.
The Event field contains information related to the sequence of
events in the request chain. The digit 1 to 6 indicates the
approximate sequence of events, and the two-letter abbreviation
is a mnemonic for the location:
1VS (vinumstrategy) shows information about the user
request on entry to vinumstrategy(). The device number
is the vinum device, and offset and length are the user
parameters. This is always the beginning of a request
sequence.
2LR (launch_requests) shows the user request just prior to
launching the low-level vinum requests in the function
launch_requests(). The parameters should be the same
as in the 1VS information.
In the following requests, Dev is the device number of the asso-
ciated disk partition, Offset is the offset from the beginning of
the partition, SD is the subdisk index in vinum_conf, SDoff is
the offset from the beginning of the subdisk, Doffset is the off-
set of the associated data request, and Goffset is the offset of
the associated group request, where applicable.
3RQ (request) shows one of possibly several low-level vinum
requests which are launched to satisfy the high-level
request. This information is also logged in
launch_requests().
4DN (done) is called from complete_rqe(), showing the com-
pletion of a request. This completion should match a
request launched either at stage 4DN from
launch_requests(), or from complete_raid5_write() at
stage 5RD or 6RP.
5RD (RAID-5 data) is called from complete_raid5_write() and
represents the data written to a RAID-5 data stripe
after calculating parity.
6RP (RAID-5 parity) is called from complete_raid5_write()
and represents the data written to a RAID-5 parity
stripe after calculating parity.
7VS shows a subdisk I/O request. These requests are usu-
ally internal to vinum for operations like initializa-
tion or rebuilding plexes.
8LR shows the low-level operation generated for a subdisk
I/O request.
Lockwait specifies that the process is waiting for a range lock.
The parameters are the buffer header associated with
the request, the plex number and the block number. For
internal reasons the block number is one higher than
the address of the beginning of the stripe.
Lock specifies that a range lock has been obtained. The
parameters are the same as for the range lock.
Unlock specifies that a range lock has been released. The
parameters are the same as for the range lock.
init [-Ssize] [-w] plex | subdiskvinuminit initializes a subdisk by writing zeroes to it. You
can initialize all subdisks in a plex by specifying the plex
name. This is the only way to ensure consistent data in a plex.
You must perform this initialization before using a RAID-5 plex.
It is also recommended for other new plexes. vinum initializes
all subdisks of a plex in parallel. Since this operation can
take a long time, it is normally performed in the background. If
you want to wait for completion of the command, use the -w (wait)
option.
Specify the -S option if you want to write blocks of a different
size from the default value of 16 kB. vinum prints a console
message when the initialization is complete.
labelvolume
The label command writes a ufs style volume label on a volume.
It is a simple alternative to an appropriate call to disklabel.
This is needed because some ufs commands still read the disk to
find the label instead of using the correct ioctl(2) call to
access it. vinum maintains a volume label separately from the
volume data, so this command is not needed for newfs(8). This
command is deprecated.
list [-r] [-V] [volume | plex | subdisk]
l [-r] [-V] [volume | plex | subdisk]
ld [-r] [-s] [-v] [-V] [volume]
ls [-r] [-s] [-v] [-V] [subdisk]
lp [-r] [-s] [-v] [-V] [plex]
lv [-r] [-s] [-v] [-V] [volume]
list is used to show information about the specified object. If
the argument is omitted, information is shown about all objects
known to vinum. The l command is a synonym for list.
The -r option relates to volumes and plexes: if specified, it
recursively lists information for the subdisks and (for a volume)
plexes subordinate to the objects. The commands lv, lp, ls and
ld list only volumes, plexes, subdisks and drives respectively.
This is particularly useful when used without parameters.
The -s option causes vinum to output device statistics, the -v
(verbose) option causes some additional information to be output,
and the -V causes considerable additional information to be out-
put.
makedev
The makedev command removes the directory /dev/vinum and recre-
ates it with device nodes which reflect the current configura-
tion. This command is not intended for general use, and is pro-
vided for emergency use only.
mirror [-f] [-nname] [-s] [-v] drives
The mirror command provides a simplified alternative to the
create command for creating mirrored volumes. Without any
options, it creates a RAID-1 (mirrored) volume with two concate-
nated plexes. The largest contiguous space available on each
drive is used to create the subdisks for the plexes. The first
plex is built from the odd-numbered drives in the list, and the
second plex is built from the even-numbered drives. If the
drives are of different sizes, the plexes will be of different
sizes.
If the -s option is provided, mirror builds striped plexes with a
stripe size of 256 kB. The size of the subdisks in each plex is
the size of the smallest contiguous storage available on any of
the drives which form the plex. Again, the plexes may differ in
size.
Normally, the mirror command creates an arbitrary name for the
volume and its components. The name is composed of the text
``vinum'' and a small integer, for example ``vinum3''. You can
override this with the -nname option, which assigns the name
specified to the volume. The plexes and subdisks are named after
the volume in the default manner.
There is no choice of name for the drives. If the drives have
already been initialized as vinum drives, the name remains. Oth-
erwise the drives are given names starting with the text
``vinumdrive'' and a small integer, for example ``vinumdrive7''.
As with the create command, the -f option can be used to specify
that a previous name should be overwritten. The -v is used to
specify verbose output.
See the section SIMPLIFIEDCONFIGURATION below for some examples
of this command.
mv-fdriveobject...move-fdriveobject...
Move all the subdisks from the specified objects onto the new
drive. The objects may be subdisks, drives or plexes. When
drives or plexes are specified, all subdisks associated with the
object are moved.
The -f option is required for this function, since it currently
does not preserve the data in the subdisk. This functionality
will be added at a later date. In this form, however, it is
suited to recovering a failed disk drive.
printconfig [file]
Write a copy of the current configuration to file in a format
that can be used to recreate the vinum configuration. Unlike the
configuration saved on disk, it includes definitions of the
drives. If you omit file, vinum writes the list to stdout.
quit Exit the vinum program when running in interactive mode. Nor-
mally this would be done by entering the EOF character.
readdisk...
The read command scans the specified disks for vinum partitions
containing previously created configuration information. It
reads the configuration in order from the most recently updated
to least recently updated configuration. vinum maintains an up-
to-date copy of all configuration information on each disk parti-
tion. You must specify all of the slices in a configuration as
the parameter to this command.
The read command is intended to selectively load a vinum configu-
ration on a system which has other vinum partitions. If you want
to start all partitions on the system, it is easier to use the
start command.
If vinum encounters any errors during this command, it will turn
off automatic configuration update to avoid corrupting the copies
on disk. This will also happen if the configuration on disk
indicates a configuration error (for example, subdisks which do
not have a valid space specification). You can turn the updates
on again with the setdaemon and saveconfig commands. Reset bit 2
(numerical value 4) of the daemon options mask to re-enable con-
figuration saves.
rebuildparityplex [-f] [-v] [-V]
Rebuild the parity blocks on the specified RAID-4 or RAID-5 plex.
This operation maintains a pointer in the plex, so it can be
stopped and later restarted from the same position if desired.
In addition, this pointer is used by the checkparity command, so
rebuilding the parity blocks need only start at the location
where the first parity problem has been detected.
If the -f flag is specified, rebuildparity starts rebuilding at
the beginning of the plex. If the -v flag is specified,
rebuildparity first checks the existing parity blocks prints
information about those found to be incorrect before rebuilding.
If the -V flag is specified, rebuildparity prints a running
progress report.
rename [-r] [drive | subdisk | plex | volume] newname
Change the name of the specified object. If the -r option is
specified, subordinate objects will be named by the default
rules: plex names will be formed by appending .pnumber to the
volume name, and subdisk names will be formed by appending
.snumber to the plex name.
resetconfig
The resetconfig command completely obliterates the vinum configu-
ration on a system. Use this command only when you want to com-
pletely delete the configuration. vinum will ask for confirma-
tion; you must type in the words NO FUTURE exactly as shown:
# vinumresetconfig
WARNING! This command will completely wipe out your vinum
configuration. All data will be lost. If you really want
to do this, enter the text
NO FUTURE
Enter text -> NOFUTURE
Vinum configuration obliterated
As the message suggests, this is a last-ditch command. Don't use
it unless you have an existing configuration which you never want
to see again.
resetstats [-r] [volume | plex | subdisk]
vinum maintains a number of statistical counters for each object.
See the header file <sys/dev/vinumvar.h> for more information.
Use the resetstats command to reset these counters. In conjunc-
tion with the -r option, vinum also resets the counters of subor-
dinate objects.
rm [-f] [-r] volume | plex | subdiskrm removes an object from the vinum configuration. Once an
object has been removed, there is no way to recover it. Normally
vinum performs a large amount of consistency checking before
removing an object. The -f option tells vinum to omit this
checking and remove the object anyway. Use this option with
great care: it can result in total loss of data on a volume.
Normally, vinum refuses to remove a volume or plex if it has sub-
ordinate plexes or subdisks respectively. You can tell vinum to
remove the object anyway by using the -f option, or you can cause
vinum to remove the subordinate objects as well by using the -r
(recursive) option. If you remove a volume with the -r option,
it will remove both the plexes and the subdisks which belong to
the plexes.
saveconfig
Save the current configuration to disk. Normally this is not
necessary, since vinum automatically saves any change in configu-
ration. If an error occurs on startup, updates will be disabled.
When you reenable them with the setdaemon command, vinum does not
automatically save the configuration to disk. Use this command
to save the configuration.
setdaemon [value]
setdaemon sets a variable bitmask for the vinum daemon. This
command is temporary and will be replaced. Currently, the bit
mask may contain the bits 1 (log every action to syslog) and 4
(don't update configuration). Option bit 4 can be useful for
error recovery.
setstatestate [volume | plex | subdisk | drive]
setstate sets the state of the specified objects to the specified
state. This bypasses the usual consistency mechanism of vinum
and should be used only for recovery purposes. It is possible to
crash the system by incorrect use of this command.
start [-iinterval] [-Ssize] [-w] [plex | subdisk]
start starts (brings into to the up state) one or more vinum
objects.
If no object names are specified, vinum scans the disks known to
the system for vinum drives and then reads in the configuration
as described under the read commands. The vinum drive contains a
header with all information about the data stored on the drive,
including the names of the other drives which are required in
order to represent plexes and volumes.
If vinum encounters any errors during this command, it will turn
off automatic configuration update to avoid corrupting the copies
on disk. This will also happen if the configuration on disk
indicates a configuration error (for example, subdisks which do
not have a valid space specification). You can turn the updates
on again with the setdaemon and saveconfig command. Reset bit 4
of the daemon options mask to re-enable configuration saves.
If object names are specified, vinum starts them. Normally this
operation is only of use with subdisks. The action depends on
the current state of the object:
+o If the object is already in the up state, vinum does nothing.
+o If the object is a subdisk in the down or reborn states,
vinum changes it to the up state.
+o If the object is a subdisk in the empty state, the change
depends on the subdisk. If it is part of a plex which is
part of a volume which contains other plexes, vinum places
the subdisk in the reviving state and attempts to copy the
data from the volume. When the operation completes, the sub-
disk is set into the up state. If it is part of a plex which
is part of a volume which contains no other plexes, or if it
is not part of a plex, vinum brings it into the up state
immediately.
+o If the object is a subdisk in the reviving state, vinum con-
tinues the revive operation offline. When the operation com-
pletes, the subdisk is set into the up state.
When a subdisk comes into the up state, vinum automatically
checks the state of any plex and volume to which it may belong
and changes their state where appropriate.
If the object is a plex, start checks the state of the subordi-
nate subdisks (and plexes in the case of a volume) and starts any
subdisks which can be started.
To start a plex in a multi-plex volume, the data must be copied
from another plex in the volume. Since this frequently takes a
long time, it is normally done in the background. If you want to
wait for this operation to complete (for example, if you are per-
forming this operation in a script), use the -w option.
Copying data doesn't just take a long time, it can also place a
significant load on the system. You can specify the transfer
size in bytes or sectors with the -S option, and an interval (in
milliseconds) to wait between copying each block with the -i
option. Both of these options lessen the load on the system.
stop [-f] [volume | plex | subdisk]
If no parameters are specified, stop removes the vinum KLD and
stops vinum(4). This can only be done if no objects are active.
In particular, the -f option does not override this requirement.
Normally, the stop command writes the current configuration back
to the drives before terminating. This will not be possible if
configuration updates are disabled, so vinum will not stop if
configuration updates are disabled. You can override this by
specifying the -f option.
The stop command can only work if vinum has been loaded as a KLD,
since it is not possible to unload a statically configured
driver. vinumstop will fail if vinum is statically configured.
If object names are specified, stop disables access to the
objects. If the objects have subordinate objects, they subordi-
nate objects must either already be inactive (stopped or in
error), or the -r and -f options must be specified. This command
does not remove the objects from the configuration. They can be
accessed again after a start command.
By default, vinum does not stop active objects. For example, you
cannot stop a plex which is attached to an active volume, and you
cannot stop a volume which is open. The -f option tells vinum to
omit this checking and remove the object anyway. Use this option
with great care and understanding: used incorrectly, it can
result in serious data corruption.
stripe [-f] [-nname] [-v] drives
The stripe command provides a simplified alternative to the
create command for creating volumes with a single striped plex.
The size of the subdisks is the size of the largest contiguous
space available on all the specified drives. The stripe size is
fixed at 256 kB.
Normally, the stripe command creates an arbitrary name for the
volume and its components. The name is composed of the text
``vinum'' and a small integer, for example ``vinum3''. You can
override this with the -nname option, which assigns the name
specified to the volume. The plexes and subdisks are named after
the volume in the default manner.
There is no choice of name for the drives. If the drives have
already been initialized as vinum drives, the name remains. Oth-
erwise the drives are given names starting with the text
``vinumdrive'' and a small integer, for example ``vinumdrive7''.
As with the create command, the -f option can be used to specify
that a previous name should be overwritten. The -v is used to
specify verbose output.
See the section SIMPLIFIEDCONFIGURATION below for some examples
of this command.
SIMPLIFIED CONFIGURATION
This section describes a simplified interface to vinum configuration
using the concat, mirror and stripe commands. These commands create con-
venient configurations for some more normal situations, but they are not
as flexible as the create command.
See above for the description of the commands. Here are some examples,
all performed with the same collection of disks. Note that the first
drive, /dev/da1h, is smaller than the others. This has an effect on the
sizes chosen for each kind of subdisk.
The following examples all use the -v option to show the commands passed
to the system, and also to list the structure of the volume. Without the
-v option, these commands produce no output.
Volumewithasingleconcatenatedplex
Use a volume with a single concatenated plex for the largest possible
storage without resilience to drive failures:
vinum -> concat -v /dev/da1h /dev/da2h /dev/da3h /dev/da4h
volume vinum0
plex name vinum0.p0 org concat
drive vinumdrive0 device /dev/da1h
sd name vinum0.p0.s0 drive vinumdrive0 size 0
drive vinumdrive1 device /dev/da2h
sd name vinum0.p0.s1 drive vinumdrive1 size 0
drive vinumdrive2 device /dev/da3h
sd name vinum0.p0.s2 drive vinumdrive2 size 0
drive vinumdrive3 device /dev/da4h
sd name vinum0.p0.s3 drive vinumdrive3 size 0
V vinum0 State: up Plexes: 1 Size: 2134 MB
P vinum0.p0 C State: up Subdisks: 4 Size: 2134 MB
S vinum0.p0.s0 State: up PO: 0 B Size: 414 MB
S vinum0.p0.s1 State: up PO: 414 MB Size: 573 MB
S vinum0.p0.s2 State: up PO: 988 MB Size: 573 MB
S vinum0.p0.s3 State: up PO: 1561 MB Size: 573 MB
In this case, the complete space on all four disks was used, giving a
volume 2134 MB in size.
Volumewithasinglestripedplex
A volume with a single striped plex may give better performance than a
concatenated plex, but restrictions on striped plexes can mean that the
volume is smaller. It will also not be resilient to a drive failure:
vinum -> stripe -v /dev/da1h /dev/da2h /dev/da3h /dev/da4h
drive vinumdrive0 device /dev/da1h
drive vinumdrive1 device /dev/da2h
drive vinumdrive2 device /dev/da3h
drive vinumdrive3 device /dev/da4h
volume vinum0
plex name vinum0.p0 org striped 256k
sd name vinum0.p0.s0 drive vinumdrive0 size 849825b
sd name vinum0.p0.s1 drive vinumdrive1 size 849825b
sd name vinum0.p0.s2 drive vinumdrive2 size 849825b
sd name vinum0.p0.s3 drive vinumdrive3 size 849825b
V vinum0 State: up Plexes: 1 Size: 1659 MB
P vinum0.p0 S State: up Subdisks: 4 Size: 1659 MB
S vinum0.p0.s0 State: up PO: 0 B Size: 414 MB
S vinum0.p0.s1 State: up PO: 256 kB Size: 414 MB
S vinum0.p0.s2 State: up PO: 512 kB Size: 414 MB
S vinum0.p0.s3 State: up PO: 768 kB Size: 414 MB
In this case, the size of the subdisks has been limited to the smallest
available disk, so the resulting volume is only 1659 MB in size.
Mirroredvolumewithtwoconcatenatedplexes
For more reliability, use a mirrored, concatenated volume:
vinum -> mirror -v -n mirror /dev/da1h /dev/da2h /dev/da3h /dev/da4h
drive vinumdrive0 device /dev/da1h
drive vinumdrive1 device /dev/da2h
drive vinumdrive2 device /dev/da3h
drive vinumdrive3 device /dev/da4h
volume mirror setupstate
plex name mirror.p0 org concat
sd name mirror.p0.s0 drive vinumdrive0 size 0b
sd name mirror.p0.s1 drive vinumdrive2 size 0b
plex name mirror.p1 org concat
sd name mirror.p1.s0 drive vinumdrive1 size 0b
sd name mirror.p1.s1 drive vinumdrive3 size 0b
V mirror State: up Plexes: 2 Size: 1146 MB
P mirror.p0 C State: up Subdisks: 2 Size: 988 MB
P mirror.p1 C State: up Subdisks: 2 Size: 1146 MB
S mirror.p0.s0 State: up PO: 0 B Size: 414 MB
S mirror.p0.s1 State: up PO: 414 MB Size: 573 MB
S mirror.p1.s0 State: up PO: 0 B Size: 573 MB
S mirror.p1.s1 State: up PO: 573 MB Size: 573 MB
This example specifies the name of the volume, mirror. Since one drive
is smaller than the others, the two plexes are of different size, and the
last 158 MB of the volume is non-resilient. To ensure complete reliabil-
ity in such a situation, use the create command to create a volume with
988 MB.
Mirroredvolumewithtwostripedplexes
Alternatively, use the -s option to create a mirrored volume with two
striped plexes:
vinum -> mirror -v -n raid10 -s /dev/da1h /dev/da2h /dev/da3h /dev/da4h
drive vinumdrive0 device /dev/da1h
drive vinumdrive1 device /dev/da2h
drive vinumdrive2 device /dev/da3h
drive vinumdrive3 device /dev/da4h
volume raid10 setupstate
plex name raid10.p0 org striped 256k
sd name raid10.p0.s0 drive vinumdrive0 size 849825b
sd name raid10.p0.s1 drive vinumdrive2 size 849825b
plex name raid10.p1 org striped 256k
sd name raid10.p1.s0 drive vinumdrive1 size 1173665b
sd name raid10.p1.s1 drive vinumdrive3 size 1173665b
V raid10 State: up Plexes: 2 Size: 1146 MB
P raid10.p0 S State: up Subdisks: 2 Size: 829 MB
P raid10.p1 S State: up Subdisks: 2 Size: 1146 MB
S raid10.p0.s0 State: up PO: 0 B Size: 414 MB
S raid10.p0.s1 State: up PO: 256 kB Size: 414 MB
S raid10.p1.s0 State: up PO: 0 B Size: 573 MB
S raid10.p1.s1 State: up PO: 256 kB Size: 573 MB
In this case, the usable part of the volume is even smaller, since the
first plex has shrunken to match the smallest drive.
CONFIGURATION FILEvinum requires that all parameters to the create commands must be in a
configuration file. Entries in the configuration file define volumes,
plexes and subdisks, and may be in free format, except that each entry
must be on a single line.
Scalefactors
Some configuration file parameters specify a size (lengths, stripe
sizes). These values can be specified as bytes, or one of the following
scale factors may be appended:
s specifies that the value is a number of sectors of 512 bytes.
k specifies that the value is a number of kilobytes (1024 bytes).
m specifies that the value is a number of megabytes (1048576
bytes).
g specifies that the value is a number of gigabytes (1073741824
bytes).
b is used for compatibility with VERITAS. It stands for blocks of
512 bytes. This abbreviation is confusing, since the word
``block'' is used in different meanings, and its use is depre-
cated.
For example, the value 16777216 bytes can also be written as 16m, 16384k
or 32768s.
The configuration file can contain the following entries:
drivenamedevicename [options]
Define a drive. The options are:
devicedevicename Specify the device on which the drive resides.
devicename must be the name of a disk parti-
tion, for example /dev/da1e or /dev/ad3s2h, and
it must be of type vinum. Do not use the ``c''
partition, which is reserved for the complete
disk.
hotspare Define the drive to be a ``hot spare'' drive,
which is maintained to automatically replace a
failed drive. vinum does not allow this drive
to be used for any other purpose. In particu-
lar, it is not possible to create subdisks on
it. This functionality has not been completely
implemented.
volumename [options]
Define a volume with name name. Options are:
plexplexname Add the specified plex to the volume. If
plexname is specified as *, vinum will look for
the definition of the plex as the next possible
entry in the configuration file after the defi-
nition of the volume.
readpolpolicy Define a readpolicy for the volume. policy
may be either round or preferplexname. vinum
satisfies a read request from only one of the
plexes. A round read policy specifies that
each read should be performed from a different
plex in round-robin fashion. A prefer read
policy reads from the specified plex every
time.
setupstate When creating a multi-plex volume, assume that
the contents of all the plexes are consistent.
This is normally not the case, so by default
vinum sets all plexes except the first one to
the faulty state. Use the start command to
first bring them to a consistent state. In the
case of striped and concatenated plexes, how-
ever, it does not normally cause problems to
leave them inconsistent: when using a volume
for a file system or a swap partition, the pre-
vious contents of the disks are not of inter-
est, so they may be ignored. If you want to
take this risk, use the setupstate keyword. It
will only apply to the plexes defined immedi-
ately after the volume in the configuration
file. If you add plexes to a volume at a later
time, you must integrate them manually with the
start command.
Note that you must use the init command with
RAID-5 plexes: otherwise extreme data corrup-
tion will result if one subdisk fails.
plex [options]
Define a plex. Unlike a volume, a plex does not need a name. The
options may be:
nameplexname Specify the name of the plex. Note that you
must use the keyword name when naming a plex or
subdisk.
orgorganization [stripesize]
Specify the organization of the plex.
organization can be one of concat, striped or
raid5. For striped and raid5 plexes, the
parameter stripesize must be specified, while
for concat it must be omitted. For type
striped, it specifies the width of each stripe.
For type raid5, it specifies the size of a
group. A group is a portion of a plex which
stores the parity bits all in the same subdisk.
It must be a factor of the plex size (in other
words, the result of dividing the plex size by
the stripe size must be an integer), and it
must be a multiple of a disk sector (512
bytes).
For optimum performance, stripes should be at
least 128 kB in size: anything smaller will
result in a significant increase in I/O activ-
ity due to mapping of individual requests over
multiple disks. The performance improvement
due to the increased number of concurrent
transfers caused by this mapping will not make
up for the performance drop due to the increase
in latency. A good guideline for stripe size
is between 256 kB and 512 kB. Avoid powers of
2, however: they tend to cause all superblocks
to be placed on the first subdisk.
A striped plex must have at least two subdisks
(otherwise it is a concatenated plex), and each
must be the same size. A RAID-5 plex must have
at least three subdisks, and each must be the
same size. In practice, a RAID-5 plex should
have at least 5 subdisks.
volumevolname Add the plex to the specified volume. If no
volume keyword is specified, the plex will be
added to the last volume mentioned in the con-
figuration file.
sdsdnameoffset Add the specified subdisk to the plex at offset
offset.
subdisk [options]
Define a subdisk. Options may be:
namename Specify the name of a subdisk. It is not nec-
essary to specify a name for a subdisk, see
OBJECTNAMING above. Note that you must spec-
ify the keyword name if you wish to name a sub-
disk.
plexoffsetoffset Specify the starting offset of the subdisk in
the plex. If not specified, vinum allocates
the space immediately after the previous sub-
disk, if any, or otherwise at the beginning of
the plex.
driveoffsetoffset Specify the starting offset of the subdisk in
the drive. If not specified, vinum allocates
the first contiguous length bytes of free space
on the drive.
lengthlength Specify the length of the subdisk. This key-
word must be specified. There is no default,
but the value 0 may be specified to mean ``use
the largest available contiguous free area on
the drive''. If the drive is empty, this means
that the entire drive will be used for the sub-
disk. length may be shortened to len.
plexplex Specify the plex to which the subdisk belongs.
By default, the subdisk belongs to the last
plex specified.
drivedrive Specify the drive on which the subdisk resides.
By default, the subdisk resides on the last
drive specified.
EXAMPLE CONFIGURATION FILE
# Sample vinum configuration file
#
# Our drives
drive drive1 device /dev/da1h
drive drive2 device /dev/da2h
drive drive3 device /dev/da3h
drive drive4 device /dev/da4h
drive drive5 device /dev/da5h
drive drive6 device /dev/da6h
# A volume with one striped plex
volume tinyvol
plex org striped 512b
sd length 64m drive drive2
sd length 64m drive drive4
volume stripe
plex org striped 512b
sd length 512m drive drive2
sd length 512m drive drive4
# Two plexes
volume concat
plex org concat
sd length 100m drive drive2
sd length 50m drive drive4
plex org concat
sd length 150m drive drive4
# A volume with one striped plex and one concatenated plex
volume strcon
plex org striped 512b
sd length 100m drive drive2
sd length 100m drive drive4
plex org concat
sd length 150m drive drive2
sd length 50m drive drive4
# a volume with a RAID-5 and a striped plex
# note that the RAID-5 volume is longer by
# the length of one subdisk
volume vol5
plex org striped 64k
sd length 1000m drive drive2
sd length 1000m drive drive4
plex org raid5 32k
sd length 500m drive drive1
sd length 500m drive drive2
sd length 500m drive drive3
sd length 500m drive drive4
sd length 500m drive drive5
DRIVE LAYOUT CONSIDERATIONSvinum drives are currently BSD disk partitions. They must be of type
vinum in order to avoid overwriting data used for other purposes. Use
disklabel-e to edit a partition type definition. The following display
shows a typical partition layout as shown by disklabel(8):
8 partitions:
# size offset fstype [fsize bsize bps/cpg]
a: 81920 344064 4.2BSD 0 0 0 # (Cyl. 240*- 297*)
b: 262144 81920 swap # (Cyl. 57*- 240*)
c: 4226725 0 unused 0 0 # (Cyl. 0 - 2955*)
e: 81920 0 4.2BSD 0 0 0 # (Cyl. 0 - 57*)
f: 1900000 425984 4.2BSD 0 0 0 # (Cyl. 297*- 1626*)
g: 1900741 2325984 vinum 0 0 0 # (Cyl. 1626*- 2955*)
In this example, partition ``g'' may be used as a vinum partition. Par-
titions ``a'', ``e'' and ``f'' may be used as UFS file systems or ccd
partitions. Partition ``b'' is a swap partition, and partition ``c''
represents the whole disk and should not be used for any other purpose.
vinum uses the first 265 sectors on each partition for configuration
information, so the maximum size of a subdisk is 265 sectors smaller than
the drive.
LOG FILEvinum maintains a log file, by default /var/tmp/vinum_history, in which
it keeps track of the commands issued to vinum. You can override the
name of this file by setting the environment variable VINUM_HISTORY to
the name of the file.
Each message in the log file is preceded by a date. The default format
is "%e %b %Y %H:%M:%S". See strftime(3) for further details of the for-
mat string. It can be overridden by the environment variable
VINUM_DATEFORMAT.
HOW TO SET UP VINUM
This section gives practical advice about how to implement a vinum sys-
tem.
Wheretoputthedata
The first choice you need to make is where to put the data. You need
dedicated disk partitions for vinum. They should be partitions, not
devices, and they should not be partition ``c''. For example, good names
are /dev/da0e or /dev/ad3s4a. Bad names are /dev/da0 and /dev/da0s1,
both of which represent a device, not a partition, and /dev/ad1c, which
represents a complete disk and should be of type unused. See the example
under DRIVELAYOUTCONSIDERATIONS above.
Designingvolumes
The way you set up vinum volumes depends on your intentions. There are a
number of possibilities:
1. You may want to join up a number of small disks to make a reasonable
sized file system. For example, if you had five small drives and
wanted to use all the space for a single volume, you might write a
configuration file like:
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
drive d4 device /dev/da5e
drive d5 device /dev/da6e
volume bigger
plex org concat
sd length 0 drive d1
sd length 0 drive d2
sd length 0 drive d3
sd length 0 drive d4
sd length 0 drive d5
In this case, you specify the length of the subdisks as 0, which
means ``use the largest area of free space that you can find on the
drive''. If the subdisk is the only subdisk on the drive, it will
use all available space.
2. You want to set up vinum to obtain additional resilience against
disk failures. You have the choice of RAID-1, also called
``mirroring'', or RAID-5, also called ``parity''.
To set up mirroring, create multiple plexes in a volume. For exam-
ple, to create a mirrored volume of 2 GB, you might create the fol-
lowing configuration file:
drive d1 device /dev/da2e
drive d2 device /dev/da3e
volume mirror
plex org concat
sd length 2g drive d1
plex org concat
sd length 2g drive d2
When creating mirrored drives, it is important to ensure that the
data from each plex is on a different physical disk so that vinum
can access the complete address space of the volume even if a drive
fails. Note that each plex requires as much data as the complete
volume: in this example, the volume has a size of 2 GB, but each
plex (and each subdisk) requires 2 GB, so the total disk storage
requirement is 4 GB.
To set up RAID-5, create a single plex of type raid5. For example,
to create an equivalent resilient volume of 2 GB, you might use the
following configuration file:
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
drive d4 device /dev/da5e
drive d5 device /dev/da6e
volume raid
plex org raid5 512k
sd length 512m drive d1
sd length 512m drive d2
sd length 512m drive d3
sd length 512m drive d4
sd length 512m drive d5
RAID-5 plexes require at least three subdisks, one of which is used
for storing parity information and is lost for data storage. The
more disks you use, the greater the proportion of the disk storage
can be used for data storage. In this example, the total storage
usage is 2.5 GB, compared to 4 GB for a mirrored configuration. If
you were to use the minimum of only three disks, you would require 3
GB to store the information, for example:
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
volume raid
plex org raid5 512k
sd length 1g drive d1
sd length 1g drive d2
sd length 1g drive d3
As with creating mirrored drives, it is important to ensure that the
data from each subdisk is on a different physical disk so that vinum
can access the complete address space of the volume even if a drive
fails.
3. You want to set up vinum to allow more concurrent access to a file
system. In many cases, access to a file system is limited by the
speed of the disk. By spreading the volume across multiple disks,
you can increase the throughput in multi-access environments. This
technique shows little or no performance improvement in single-
access environments. vinum uses a technique called ``striping'', or
sometimes RAID-0, to increase this concurrency of access. The name
RAID-0 is misleading: striping does not provide any redundancy or
additional reliability. In fact, it decreases the reliability,
since the failure of a single disk will render the volume useless,
and the more disks you have, the more likely it is that one of them
will fail.
To implement striping, use a striped plex:
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
drive d4 device /dev/da5e
volume raid
plex org striped 512k
sd length 512m drive d1
sd length 512m drive d2
sd length 512m drive d3
sd length 512m drive d4
A striped plex must have at least two subdisks, but the increase in
performance is greater if you have a larger number of disks.
4. You may want to have the best of both worlds and have both
resilience and performance. This is sometimes called RAID-10 (a
combination of RAID-1 and RAID-0), though again this name is mis-
leading. With vinum you can do this with the following configura-
tion file:
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
drive d4 device /dev/da5e
volume raid setupstate
plex org striped 512k
sd length 512m drive d1
sd length 512m drive d2
sd length 512m drive d3
sd length 512m drive d4
plex org striped 512k
sd length 512m drive d4
sd length 512m drive d3
sd length 512m drive d2
sd length 512m drive d1
Here the plexes are striped, increasing performance, and there are
two of them, increasing reliability. Note that this example shows
the subdisks of the second plex in reverse order from the first
plex. This is for performance reasons and will be discussed below.
In addition, the volume specification includes the keyword
setupstate, which ensures that all plexes are up after creation.
Creatingthevolumes
Once you have created your configuration files, start vinum and create
the volumes. In this example, the configuration is in the file
configfile:
# vinum create -v configfile
1: drive d1 device /dev/da2e
2: drive d2 device /dev/da3e
3: volume mirror
4: plex org concat
5: sd length 2g drive d1
6: plex org concat
7: sd length 2g drive d2
Configuration summary
Drives: 2 (4 configured)
Volumes: 1 (4 configured)
Plexes: 2 (8 configured)
Subdisks: 2 (16 configured)
Drive d1: Device /dev/da2e
Created on vinum.lemis.com at Tue Mar 23 12:30:31 1999
Config last updated Tue Mar 23 14:30:32 1999
Size: 60105216000 bytes (57320 MB)
Used: 2147619328 bytes (2048 MB)
Available: 57957596672 bytes (55272 MB)
State: up
Last error: none
Drive d2: Device /dev/da3e
Created on vinum.lemis.com at Tue Mar 23 12:30:32 1999
Config last updated Tue Mar 23 14:30:33 1999
Size: 60105216000 bytes (57320 MB)
Used: 2147619328 bytes (2048 MB)
Available: 57957596672 bytes (55272 MB)
State: up
Last error: none
Volume mirror: Size: 2147483648 bytes (2048 MB)
State: up
Flags:
2 plexes
Read policy: round robin
Plex mirror.p0: Size: 2147483648 bytes (2048 MB)
Subdisks: 1
State: up
Organization: concat
Part of volume mirror
Plex mirror.p1: Size: 2147483648 bytes (2048 MB)
Subdisks: 1
State: up
Organization: concat
Part of volume mirror
Subdisk mirror.p0.s0:
Size: 2147483648 bytes (2048 MB)
State: up
Plex mirror.p0 at offset 0
Subdisk mirror.p1.s0:
Size: 2147483648 bytes (2048 MB)
State: up
Plex mirror.p1 at offset 0
The -v option tells vinum to list the file as it configures. Subse-
quently it lists the current configuration in the same format as the list-v command.
Creatingmorevolumes
Once you have created the vinum volumes, vinum keeps track of them in its
internal configuration files. You do not need to create them again. In
particular, if you run the create command again, you will create addi-
tional objects:
# vinum create sampleconfig
Configuration summary
Drives: 2 (4 configured)
Volumes: 1 (4 configured)
Plexes: 4 (8 configured)
Subdisks: 4 (16 configured)
D d1 State: up Device /dev/da2e Avail: 53224/57320 MB (92%)
D d2 State: up Device /dev/da3e Avail: 53224/57320 MB (92%)
V mirror State: up Plexes: 4 Size: 2048 MB
P mirror.p0 C State: up Subdisks: 1 Size: 2048 MB
P mirror.p1 C State: up Subdisks: 1 Size: 2048 MB
P mirror.p2 C State: up Subdisks: 1 Size: 2048 MB
P mirror.p3 C State: up Subdisks: 1 Size: 2048 MB
S mirror.p0.s0 State: up PO: 0 B Size: 2048 MB
S mirror.p1.s0 State: up PO: 0 B Size: 2048 MB
S mirror.p2.s0 State: up PO: 0 B Size: 2048 MB
S mirror.p3.s0 State: up PO: 0 B Size: 2048 MB
As this example (this time with the -f option) shows, re-running the
create has created four new plexes, each with a new subdisk. If you want
to add other volumes, create new configuration files for them. They do
not need to reference the drives that vinum already knows about. For
example, to create a volume raid on the four drives /dev/da1e, /dev/da2e,
/dev/da3e and /dev/da4e, you only need to mention the other two:
drive d3 device /dev/da1e
drive d4 device /dev/da4e
volume raid
plex org raid5 512k
sd size 2g drive d1
sd size 2g drive d2
sd size 2g drive d3
sd size 2g drive d4
With this configuration file, we get:
# vinum create newconfig
Configuration summary
Drives: 4 (4 configured)
Volumes: 2 (4 configured)
Plexes: 5 (8 configured)
Subdisks: 8 (16 configured)
D d1 State: up Device /dev/da2e Avail: 51176/57320 MB (89%)
D d2 State: up Device /dev/da3e Avail: 53220/57320 MB (89%)
D d3 State: up Device /dev/da1e Avail: 53224/57320 MB (92%)
D d4 State: up Device /dev/da4e Avail: 53224/57320 MB (92%)
V mirror State: down Plexes: 4 Size: 2048 MB
V raid State: down Plexes: 1 Size: 6144 MB
P mirror.p0 C State: init Subdisks: 1 Size: 2048 MB
P mirror.p1 C State: init Subdisks: 1 Size: 2048 MB
P mirror.p2 C State: init Subdisks: 1 Size: 2048 MB
P mirror.p3 C State: init Subdisks: 1 Size: 2048 MB
P raid.p0 R5 State: init Subdisks: 4 Size: 6144 MB
S mirror.p0.s0 State: up PO: 0 B Size: 2048 MB
S mirror.p1.s0 State: up PO: 0 B Size: 2048 MB
S mirror.p2.s0 State: up PO: 0 B Size: 2048 MB
S mirror.p3.s0 State: up PO: 0 B Size: 2048 MB
S raid.p0.s0 State: empty PO: 0 B Size: 2048 MB
S raid.p0.s1 State: empty PO: 512 kB Size: 2048 MB
S raid.p0.s2 State: empty PO: 1024 kB Size: 2048 MB
S raid.p0.s3 State: empty PO: 1536 kB Size: 2048 MB
Note the size of the RAID-5 plex: it is only 6 GB, although together its
components use 8 GB of disk space. This is because the equivalent of one
subdisk is used for storing parity data.
RestartingVinum
On rebooting the system, start vinum with the start command:
# vinum start
This will start all the vinum drives in the system. If for some reason
you wish to start only some of them, use the read command.
Performanceconsiderations
A number of misconceptions exist about how to set up a RAID array for
best performance. In particular, most systems use far too small a stripe
size. The following discussion applies to all RAID systems, not just to
vinum.
The FreeBSD block I/O system issues requests of between .5kB and 128 kB;
a typical mix is somewhere round 8 kB. You can't stop any striping sys-
tem from breaking a request into two physical requests, and if you make
the stripe small enough, it can be broken into several. This will result
in a significant drop in performance: the decrease in transfer time per
disk is offset by the order of magnitude greater increase in latency.
With modern disk sizes and the FreeBSD I/O system, you can expect to have
a reasonably small number of fragmented requests with a stripe size
between 256 kB and 512 kB; with correct RAID implementations there is no
obvious reason not to increase the size to 2 or 4 MB on a large disk.
When choosing a stripe size, consider that most current UFS file systems
have cylinder groups 32 MB in size. If you have a stripe size and number
of disks both of which are a power of two, it is probable that all
superblocks and inodes will be placed on the same subdisk, which will
impact performance significantly. Choose an odd number instead, for
example 479 kB.
The easiest way to consider the impact of any transfer in a multi-access
system is to look at it from the point of view of the potential bottle-
neck, the disk subsystem: how much total disk time does the transfer use?
Since just about everything is cached, the time relationship between the
request and its completion is not so important: the important parameter
is the total time that the request keeps the disks active, the time when
the disks are not available to perform other transfers. As a result, it
doesn't really matter if the transfers are happening at the same time or
different times. In practical terms, the time we're looking at is the
sum of the total latency (positioning time and rotational latency, or the
time it takes for the data to arrive under the disk heads) and the total
transfer time. For a given transfer to disks of the same speed, the
transfer time depends only on the total size of the transfer.
Consider a typical news article or web page of 24 kB, which will probably
be read in a single I/O. Take disks with a transfer rate of 6 MB/s and
an average positioning time of 8 ms, and a file system with 4 kB blocks.
Since it's 24 kB, we don't have to worry about fragments, so the file
will start on a 4 kB boundary. The number of transfers required depends
on where the block starts: it's (S + F - 1) / S, where S is the stripe
size in file system blocks, and F is the file size in file system blocks.
1. Stripe size of 4 kB. You'll have 6 transfers. Total subsystem
load: 48 ms latency, 2 ms transfer, 50 ms total.
2. Stripe size of 8 kB. On average, you'll have 3.5 transfers. Total
subsystem load: 28 ms latency, 2 ms transfer, 30 ms total.
3. Stripe size of 16 kB. On average, you'll have 2.25 transfers.
Total subsystem load: 18 ms latency, 2 ms transfer, 20 ms total.
4. Stripe size of 256 kB. On average, you'll have 1.08 transfers.
Total subsystem load: 8.6 ms latency, 2 ms transfer, 10.6 ms total.
5. Stripe size of 4 MB. On average, you'll have 1.0009 transfers.
Total subsystem load: 8.01 ms latency, 2 ms transfer, 10.01 ms
total.
It appears that some hardware RAID systems have problems with large
stripes: they appear to always transfer a complete stripe to or from
disk, so that a large stripe size will have an adverse effect on perfor-
mance. vinum does not suffer from this problem: it optimizes all disk
transfers and does not transfer unneeded data.
Note that no well-known benchmark program tests true multi-access condi-
tions (more than 100 concurrent users), so it is difficult to demonstrate
the validity of these statements.
Given these considerations, the following factors affect the performance
of a vinum volume:
+o Striping improves performance for multiple access only, since it
increases the chance of individual requests being on different
drives.
+o Concatenating UFS file systems across multiple drives can also
improve performance for multiple file access, since UFS divides a
file system into cylinder groups and attempts to keep files in a sin-
gle cylinder group. In general, it is not as effective as striping.
+o Mirroring can improve multi-access performance for reads, since by
default vinum issues consecutive reads to consecutive plexes.
+o Mirroring decreases performance for all writes, whether multi-access
or single access, since the data must be written to both plexes.
This explains the subdisk layout in the example of a mirroring con-
figuration above: if the corresponding subdisk in each plex is on a
different physical disk, the write commands can be issued in paral-
lel, whereas if they are on the same physical disk, they will be per-
formed sequentially.
+o RAID-5 reads have essentially the same considerations as striped
reads, unless the striped plex is part of a mirrored volume, in which
case the performance of the mirrored volume will be better.
+o RAID-5 writes are approximately 25% of the speed of striped writes:
to perform the write, vinum must first read the data block and the
corresponding parity block, perform some calculations and write back
the parity block and the data block, four times as many transfers as
for writing a striped plex. On the other hand, this is offset by the
cost of mirroring, so writes to a volume with a single RAID-5 plex
are approximately half the speed of writes to a correctly configured
volume with two striped plexes.
+o When the vinum configuration changes (for example, adding or removing
objects, or the change of state of one of the objects), vinum writes
up to 128 kB of updated configuration to each drive. The larger the
number of drives, the longer this takes.
CreatingfilesystemsonVinumvolumes
You do not need to run disklabel(8) before creating a file system on a
vinum volume. Just run newfs(8). Use the -v option to state that the
device is not divided into partitions. For example, to create a file
system on volume mirror, enter the following command:
# newfs -v /dev/vinum/mirror
A number of other considerations apply to vinum configuration:
+o There is no advantage in creating multiple drives on a single disk.
Each drive uses 131.5 kB of data for label and configuration informa-
tion, and performance will suffer when the configuration changes.
Use appropriately sized subdisks instead.
+o It is possible to increase the size of a concatenated vinum plex, but
currently the size of striped and RAID-5 plexes cannot be increased.
Currently the size of an existing UFS file system also cannot be
increased, but it is planned to make both plexes and file systems
extensible.
STATE MANAGEMENT
Vinum objects have the concept of state. See vinum(4) for more details.
They are only completely accessible if their state is up. To change an
object state to up, use the start command. To change an object state to
down, use the stop command. Normally other states are created automati-
cally by the relationship between objects. For example, if you add a
plex to a volume, the subdisks of the plex will be set in the empty
state, indicating that, though the hardware is accessible, the data on
the subdisk is invalid. As a result of this state, the plex will be set
in the faulty state.
The`reviving'state
In many cases, when you start a subdisk the system must copy data to the
subdisk. Depending on the size of the subdisk, this can take a long
time. During this time, the subdisk is set in the reviving state. On
successful completion of the copy operation, it is automatically set to
the up state. It is possible for the process performing the revive to be
stopped and restarted. The system keeps track of how far the subdisk has
been revived, and when the start command is reissued, the copying contin-
ues from this point.
In order to maintain the consistency of a volume while one or more of its
plexes is being revived, vinum writes to subdisks which have been revived
up to the point of the write. It may also read from the plex if the area
being read has already been revived.
GOTCHAS
The following points are not bugs, and they have good reasons for exist-
ing, but they have shown to cause confusion. Each is discussed in the
appropriate section above.
1. vinum drives are UNIX disk partitions and must have the partition
type vinum. This is different from ccd(4), which expects partitions
of type 4.2BSD. This behaviour of ccd is an invitation to shoot
yourself in the foot: with ccd you can easily overwrite a file sys-
tem. vinum will not permit this.
For similar reasons, the vinumstart command will not accept a drive
on partition ``c''. Partition ``c'' is used by the system to repre-
sent the whole disk, and must be of type unused. Clearly there is a
conflict here, which vinum resolves by not using the ``c'' parti-
tion.
2. When you create a volume with multiple plexes, vinum does not auto-
matically initialize the plexes. This means that the contents are
not known, but they are certainly not consistent. As a result, by
default vinum sets the state of all newly-created plexes except the
first to faulty. In order to synchronize them with the first plex,
you must start them, which causes vinum to copy the data from a plex
which is in the up state. Depending on the size of the subdisks
involved, this can take a long time.
In practice, people aren't too interested in what was in the plex
when it was created, and other volume managers cheat by setting them
up anyway. vinum provides two ways to ensure that newly created
plexes are up:
+o Create the plexes and then synchronize them with vinumstart.
+o Create the volume (not the plex) with the keyword setupstate,
which tells vinum to ignore any possible inconsistency and set
the plexes to be up.
3. Some of the commands currently supported by vinum are not really
needed. For reasons which I don't understand, however, I find that
users frequently try the label and resetconfig commands, though
especially resetconfig outputs all sort of dire warnings. Don't use
these commands unless you have a good reason to do so.
4. Some state transitions are not very intuitive. In fact, it's not
clear whether this is a bug or a feature. If you find that you
can't start an object in some strange state, such as a reborn sub-
disk, try first to get it into stopped state, with the stop or stop-f commands. If that works, you should then be able to start it.
If you find that this is the only way to get out of a position where
easier methods fail, please report the situation.
5. If you build the kernel module with the -DVINUMDEBUG option, you
must also build vinum with the -DVINUMDEBUG option, since the size
of some data objects used by both components depends on this option.
If you don't do so, commands will fail with the message Invalidargument, and a console message will be logged such as
vinumioctl:invalidioctlfromprocess247(vinum):c0e44642
This error may also occur if you use old versions of KLD or userland
program.
6. The vinumread command has a particularly emetic syntax. Once it
was the only way to start vinum, but now the preferred method is
with vinumstart. vinumread should be used for maintenance pur-
poses only. Note that its syntax has changed, and the arguments
must be disk slices, such as /dev/da0, not partitions such as
/dev/da0e.
FILES
/dev/vinum directory with device nodes for vinum objects
/dev/vinum/control control device for vinum
/dev/vinum/plex directory containing device nodes for vinum plexes
/dev/vinum/sd directory containing device nodes for vinum subdisks
ENVIRONMENT
VINUM_HISTORY The name of the log file, by default
/var/log/vinum_history.
VINUM_DATEFORMAT The format of dates in the log file, by default "%e %b
%Y %H:%M:%S".
EDITOR The name of the editor to use for editing configuration
files, by default vi.
SEE ALSOstrftime(3), vinum(4), disklabel(8), newfs(8)http://www.vinumvm.org/vinum/,
http://www.vinumvm.org/vinum/how-to-debug.html.
AUTHORS
Greg Lehey <grog@lemis.com>
HISTORY
The vinum command first appeared in FreeBSD 3.0. The RAID-5 component of
vinum was developed for Cybernet Inc. (www.cybernet.com) for its NetMAX
product.
FreeBSD 4.10 December 20, 2000 FreeBSD 4.10